Electrostatic discharge protection for electrostatically actuated microrelays

ABSTRACT

Apparatus and methods for protecting devices such as micro-switches ( 100 ) and micro-relays from adverse effects of electrostatic discharge (ESD). A protection device is provided that includes a two terminal switch ( 102, 104 ) that can be actuated by an ESD event to protect an EDS-sensitive micro-switch or micro-relay from potential malfunction and/or damage. The two terminal switch is configured to close in less time than the micro-switch or micro-relay it is protecting, thereby disipating the energy associated with the ESD event without causing damage to the micro-relays which are provided with increased immunity to the adverse effects of ESD events. The micro-switch includes respective drain/gate terminal pairs at respective ends of the device. The micro-relay includes at least two drain terminals ( 106 ) and a gate terminal ( 102 ) at respective ends of the device. The micro-switch and micro-relay are configured to be less sensitive to ESD events by using the gate terminal ( 104 ) at one end of the device to latch that end of the device down, thereby increasing the gate or drain voltage required to generate a threshold electric field to pull the other end of the device down.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority of U.S. Provisional PatentApplication No. 60/188,121 filed Mar. 9, 2000 entitled ELECTROSTATICDISCHARGE PROTECTION FOR ELECTROSTATICALLY ACTUATED MICRORELAYS.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0002] N/A

BACKGROUND OF THE INVENTION

[0003] The present invention relates generally to micro-mechanicalswitches and relays, and more specifically to electro-staticallyactuated micro-switches and micro-relays that have reducedsusceptibility to malfunction and/or damage from electrostaticdischarge. The present invention further relates to protection devicesfor protecting electro-statically actuated micro-switches andmicro-relays from adverse effects of electrostatic discharge.

[0004] Micro-mechanical switches and relays (also known asmicro-switches and micro-relays) are frequently employed to routesignals in electronic devices and systems. Such micro-switches andmicro-relays typically comprise at least one source terminal, at leastone gate terminal, at least one drain terminal, and various style beamsmounted to a substrate. A respective beam is controlled by the gateterminal for selectively connecting the source terminal to the drainterminal (as in a conventional micro-switch device) or for selectivelyconnecting two (2) drain terminals (as in a conventional micro-relaydevice). Such micro-switch and micro-relay devices are described in U.S.Pat. No. 6,153,839 issued Nov. 28, 2000 entitled MICRO-MECHANICALSWITCHING DEVICES.

[0005] In recent years, micro-switch and micro-relay devices have becomeincreasingly susceptible to malfunction and/or damage from applicationof excessive voltages resulting from, e.g., electrostatic discharge(ESD). This is due at least in part to the decreasing sizes of thedevices as circuit geometries are scaled down.

[0006] During the manufacture and assembly of micro-switch andmicro-relay devices, all terminals of the devices are typicallyESD-sensitive. For example, electrostatic charge may be transferred fromone or more terminals of a micro-switch or micro-relay device to anotherconducting object during the manufacture or assembly of the device. Thischarge may generate voltages that are large enough to cause the deviceto malfunction, breakdown the gate oxide on the device, or dissipatesufficient energy to produce electro-thermal failures in the device.

[0007] Moreover, when micro-switch and micro-relay devices are beingused in the field, one or more drain terminals of the devices are oftenused to connect internal systems, which may be implemented on the samesubstrate as the device, to external systems. This exposes the drainterminals to potential ESD that may cause malfunction in and/or damageto the devices.

[0008] One approach to reducing the adverse effects of ESD during themanufacture and assembly of micro-switches and micro-relays is torequire special handling of these devices. For example, such specialhandling may involve proper grounding of manufacturing and assemblypersonnel who come in contact with the devices, and/or the use ofESD-resistant containers for transporting the devices during themanufacturing and assembly processes. However, such specialized devicehandling is often expensive to implement and may increase manufacturingand assembly costs.

[0009] Another approach to reducing the effects of ESD not only duringthe manufacture and assembly of micro-switches and micro-relays but alsowhen these devices are in-use is to have ESD protection built into theintegrated circuits containing the devices. However, conventional ESDprotection techniques used in integrated circuits, in general, are notalways suitable for protecting micro-switch and micro-relay devicestructures. This may be because of constraints in the manufacturingprocess, or because the conventional ESD protection techniques maydisturb the signal to be switched.

[0010] It would therefore be desirable to have devices such asmicro-switches and micro-relays that are less susceptible to the adverseeffects of ESD. Such devices would have reduced susceptibility tomalfunction and/or damage from ESD during the manufacture and assemblyof the devices and when the devices are being used in the field. Itwould also be desirable to have ESD protection devices that are suitablefor protecting micro-switches and micro-relays.

BRIEF SUMMARY OF THE INVENTION

[0011] Apparatus and methods for protecting devices such asmicro-switches and micro-relays from adverse effects of electrostaticdischarge (ESD) are provided. In a first embodiment, a protection deviceis provided that includes a two (2) terminal switch that can be actuatedby an ESD event to protect an ESD-sensitive micro-switch or micro-relayfrom potential malfunction and/or damage. The two (2) terminal switch isconfigured to close in less time than the micro-switch or micro-relay itis protecting, thereby dissipating the energy associated with the ESDevent without causing damage to the micro-switch or micro-relay. In oneembodiment, the two (2) terminal switch includes a source terminal, adrain terminal, and a beam mounted on a substrate. The drain terminalincludes at least one drain contact, and the beam includes a first endattached to the source terminal and a second end overhanging the draincontact to define a drain contact overlap area. In a preferredembodiment, the drain contact overlap area of the protection device isconfigured to allow the two (2) terminal switch to close at apredetermined voltage and in less time than the micro-switch ormicro-relay it is protecting.

[0012] The at least one drain contact of the protection device isconfigured to withstand the potentially damaging effects of the ESDevent. In one embodiment, a respective current-limiting resistor inseries with the at least one drain contact is employed in the protectiondevice. In another embodiment, the protection device includes at leastone first drain contact in a primary conducting path, at least onesecond drain contact in a high resistance path in parallel with theprimary conducting path, and a respective current-limiting resistor inseries with the at least one second drain contact. Respective draincontact overlap areas associated with the first and second draincontacts are configured to allow the high resistance path to closebefore the primary conducting path, thereby allowing the primaryconducting path to close safely to provide a low resistance path forcurrent flow. In alternative embodiments, increased numbers of draincontacts and/or different drain contact compositions are used in theprotection device to resist damage from the ESD event.

[0013] In still another embodiment of the protection device, a gateterminal is employed to bias the two (2) terminal switch to make closureof the switch faster. The gate terminal can be further employed as athird terminal to maintain actuation of the two (2) terminal switchwhile the drain terminal removes excess electrostatic charge.

[0014] In a second embodiment, micro-switches and micro-relays areprovided with increased immunity to the adverse effects of ESD events.The micro-switch includes respective drain/gate terminal pairs atrespective ends of the device. The micro-relay includes at least two (2)drain terminals and a gate terminal at respective ends of the device.The micro-switch and micro-relay are configured to be less sensitive toESD events by using the gate terminal at one end of the device to latchthat end of the device down, thereby increasing the gate or drainvoltage required to generate a threshold electric field to pull theother end of the device down. In alternative embodiments, this gate ordrain voltage is further increased by adding contacts and/or bumpers toprevent contact between the beam and the gate terminal at thelatched-down end of the device.

[0015] Other features, functions, and aspects of the invention will beevident from the Detailed Description of the Invention that follows.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

[0016] The invention will be more fully understood with reference to thefollowing Detailed Description of the Invention in conjunction with thedrawings of which:

[0017]FIG. 1a is a top view of a conventional micro-switch;

[0018]FIG. 1b is a perspective view of the conventional micro-switch ofFIG. 1a;

[0019]FIG. 2a is a top view of a conventional micro-relay;

[0020]FIG. 2b is a side view of the conventional micro-relay of FIG. 2a;

[0021]FIG. 3 is a top view of an electrostatic discharge protectiondevice for protecting the micro-switch and micro-relay of FIGS. 1 and 2,in accordance with the present invention;

[0022]FIG. 4 is a top view of a micro-switch configured for reducingsensitivity to electrostatic discharge, in accordance with the presentinvention;

[0023]FIG. 5 is a top view of a conventional ganged switch having commonbeam, common source, common gate, and common drain terminals;

[0024]FIG. 6 is a top view of a conventional ganged switch havingmultiple beams and common source, common gate, and common drainterminals;

[0025]FIG. 7 is a top view of the ganged switch of FIG. 5 includingintegral resistors for reducing sensitivity to electrostatic discharge,in accordance with the present invention; and

[0026]FIG. 8 is a top view of the ganged switch of FIG. 6 includingintegral resistors for reducing sensitivity to electrostatic discharge,in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0027] U.S. Provisional Patent Application No. 60/188,121 filed Mar. 9,2000 is incorporated herein by reference.

[0028] Apparatus and methods are disclosed for protectingmicro-mechanical switches and relays (also known as micro-switches andmicro-relays) from adverse effects of electrostatic discharge (ESD). Inone embodiment, the presently disclosed apparatus comprises a protectiondevice for protecting a micro-switch or micro-relay from potentiallydamaging ESD events. The protection device is a passive device includinga two (2) terminal switch that is actuated by an ESD event. The two (2)terminal switch is configured to close in less time than themicro-switch or micro-relay it is protecting, thereby dissipating energyassociated with the ESD event that might otherwise cause malfunction inand/or damage to the micro-switch or micro-relay.

[0029] In another embodiment, the presently disclosed apparatuscomprises a micro-switch and micro-relay with increased immunity to ESD.Each micro-switch and micro-relay includes a gate terminal and at leastone drain terminal at respective ends of the device. The micro-switchand micro-relay are configured to be less sensitive to ESD events byusing the gate terminal at one end of the device to latch that end ofthe device down. Such a configuration increases the “pull-in voltage”required to generate a threshold electric field to pull the other end ofthe device down, thereby reducing the device's susceptibility tomalfunction and damage during ESD events.

[0030]FIGS. 1a and 1 b depict a conventional micro-switch 100 comprisinga source terminal 102, a gate terminal 104, a drain terminal 106, and aconductive beam 108 mounted to a substrate (not shown). As shown in FIG.1b, the beam 108 includes a fixed portion 108 a fixedly attached to thesource terminal 102 at a proximal end of the beam 108, and a contactportion 108 c overhanging the gate terminal 104 at a distal end of thebeam 108. It should be noted that at least the tip of the contactportion 108 c overhangs the drain terminal 106. In the illustratedembodiment, the portion of the beam 108 extending from the sourceterminal 102 is split into two (2) parts and includes two (2) flexures108 b (see FIG. 1b).

[0031] The main part of the beam 108 is configured to be more rigid thanthe flexures 108 b. Such rigidity of the main part of the beam 108 actsto prevent contact between the contact portion 108 c of the beam 108 andthe gate terminal 104, thereby improving the over-voltage factor of themicro-switch 100. It is noted that the over-voltage factor of amicro-switch or micro-relay may be defined as the ratio between thevoltage at which the device's beam is pulled into contact with the gateterminal (causing the device to malfunction), and the voltage at whichthe beam is pulled into contact with the drain terminal. Theover-voltage factor is typically employed to define the maximum voltagethat a micro-switch or micro-relay can safely withstand.

[0032] The over-voltage factor of the micro-switch 100 is furtherimproved by positioning the gate terminal 104 near the distal end of thebeam 108 and the drain terminal 106, and by positioning drain contacts106 a-106 b of the drain terminal 106 in the area defined by the gateterminal 104. During actuation of the micro-switch 100, thisconfiguration reduces the electrostatic forces acting near the center ofthe beam 108 relative to the electrostatic forces acting near thecontact portion 108 c of the beam 108.

[0033] As described above, at least the tip of the contact portion 108 cof the beam 108 overhangs the drain terminal 106. During actuation ofthe micro-switch 100, the contact portion 108 c comes into mechanicaland electrical contact with the drain contacts 106 a-106 b to completethe circuit between the source terminal 102 and the drain terminal 106.Specifically, when an appropriate pull-in voltage is applied to the gateterminal 104, an electric field is established in the space between thegate terminal 104 and the contact portion 108 c. When the electric fieldreaches a threshold value, the beam 108 deflects toward the drainterminal 106 until the contact portion 108 c comes into contact with thedrain contacts 106 a-106 b, thereby completing the circuit between thesource terminal 102 and the drain terminal 106.

[0034] The micro-switch 100 may be packaged for interconnection toexternal circuitry (not shown). For example, bonding wires may connectthe terminals 102, 104, and 106 to respective bonding pads mounted tothe substrate. Further, printed circuit interconnections or additionalbonding wires may connect the bonding pads to the external circuitry. Ametalization layer may also be used to connect the micro-switch 100 tointernal circuitry (not shown), e.g., a transistor, which may be formedon the substrate.

[0035]FIGS. 2a and 2 b depict a conventional micro-relay 200 comprisinga source terminal 202, a gate terminal 204, a first drain terminal 206,a second drain terminal 207, and a beam 208 mounted to a substrate (notshown). As shown in FIG. 2b, the beam 208 includes a fixed portion 208 afixedly attached to the source terminal 202 at a proximal end of thebeam 208, and an insulative portion 208 d overhanging the gate terminal204 and the drain terminals 206 and 207 at a distal end of the beam 208.In the illustrated embodiment, the portion of the beam 208 extendingfrom the source terminal 202 is split into two (2) parts and includestwo (2) flexures 208 b (see FIG. 2b). The insulative portion 208 delectrically insulates the main part of the beam 208 from a contactportion 208 c provided on a surface of the insulative portion 208 dconfronting drain contacts 206 a and 207 a.

[0036] Like the micro-switch 100, the micro-relay 200 comprises featuresthat improve the over-voltage factor of the device. Specifically, themain part of the beam 208 is configured to be more rigid than theflexures 208 b to prevent contact between the contact portion 208 c andthe gate terminal 204. Further, the gate terminal 204 is positioned nearthe distal end of the beam 208 and the drain terminals 206 and 207, andthe drain contacts 206 a and 207 b are positioned in areas defined bythe gate terminal 204 to reduce the electrostatic forces acting near thecenter of the beam 208 relative to the electrostatic forces acting nearthe contact portion 208 c of the beam 208 during actuation of themicro-relay 200.

[0037] The contact portion 208 c of the beam 208 confronts the draincontacts 206 a and 207 a and is capable of coming into mechanical andelectrical contact with the drain contacts 206 a and 207 a to form anelectrical connection therebetween. Specifically, when an appropriatepull-in voltage is applied to the gate terminal 204, an electric fieldis established in the space between the contact portion 208 c of thebeam 208 and the gate terminal 204. When the electric field reaches athreshold value, the beam 208 deflects toward the drain terminals 206and 207 until the contact portion 208 c comes into contact with thedrain contacts 206 a and 207 a, thereby forming the electricalconnection between the two (2) drain contacts 206 a and 207 a. It isnoted that the insulative portion 208 d of the beam 208 allows actuationof the micro-relay 200 independent of the drain contacts 206 a and 207a.

[0038]FIG. 3 depicts a top view of an ESD protection device 300 that canbe employed to protect devices such as the micro-switch 100 (see FIGS.1a-1 b) and the micro-relay 200 (see FIGS. 2a-2 b) from the adverseeffects of ESD, in accordance with the present invention. The ESDprotection device 300 comprises a passive, two (2) terminal switchincluding a source terminal 302, a drain terminal 306, and a beam 308mounted to a substrate (not shown). Like the beam 108 of themicro-switch 100 (see FIGS. 1a-1 b), the beam 308 of the ESD protectiondevice 300 includes a fixed portion 308 a fixedly attached to the sourceterminal 302 at a proximal end of the beam 308, and a contact portion308 c at least the tip of which overhangs the drain contacts 306 a-306 bat a distal end of the beam 308. Further, in a preferred embodiment, theportion of the beam 308 extending from the source terminal 302 is splitinto two (2) parts and includes two (2) flexures 308 b. During actuationof the ESD protection device 300, the split portion reduceselectrostatic forces acting near the center of the beam 308 relative toelectrostatic forces acting near the contact portion 308 c of the beam308.

[0039] According to the present invention, the ESD protection device 300is actuated in response to an ESD event to protect devices such as themicro-switch 100 (see FIGS. 1a-1 b) and the micro-relay 200 (see FIGS.2a-2 b) from potential malfunction and/or damage due to the ESD event.For example, during the manufacture and assembly of the micro-switch 100or micro-relay 200, an ESD event may cause an electrostatic charge to betransferred from one or more terminals of the device to anotherconducting object. Such an electrostatic charge may generate voltagesthat are large enough to cause the device to malfunction, breakdown thegate oxide of the device, or dissipate enough energy to produceelectro-thermal failures in the device. Moreover, when the micro-switch100 or micro-relay 200 is being used in the field, one or more drainterminals of the device may be used to connect internal systemsimplemented, e.g., on the same substrate as the device, to one or moreexternal systems. This exposes the drain terminal of the micro-switch100 or micro-relay 200 to potential ESD events that may causemalfunction in and/or damage to the device.

[0040] The two (2) terminal switch of the ESD protection device 300 isconfigured to close, in response to an ESD event, in less time than thedevice(s) it is protecting, thereby dissipating energy associated withthe ESD event without causing malfunction in and/or damage to theprotected device(s). Specifically, an ESD event causes a pull-in voltageto be generated at the source terminal 302 or the drain terminal 306 ofthe ESD protection device 300, thereby establishing an electric field inthe space between the contact portion 308 c of the beam 308 and thedrain contacts 306 a-306 b. When the electric field reaches a thresholdvalue, the beam 308 deflects until the contact portion 308 c comes intomechanical and electrical contact with the drain contacts 306 a-306 b,thereby completing the circuit between the source terminal 302 and thedrain terminal 306.

[0041] As described above, at least the tip of the contact portion 308 cof the ESD protection device 300 overhangs the drain contacts 306 a-306b of the drain terminal 306. In a preferred embodiment, the resultingoverlap area of the drain contacts 306 a-306 b is configured to allowthe two (2) terminal switch of the ESD protection device 300 to close ata predetermined voltage and in less time than the device(s) it isprotecting.

[0042] The operation of the ESD protection device 300 will be betterunderstood with reference to the following first illustrative example.In this first example, it is understood that the ESD protection device300 is employed to protect the micro-switch 100 from adverse effects ofan ESD event. It is further understood that the source terminal 302 ofthe ESD protection device 300 is electrically connected to the sourceterminal 102 of the micro-switch 100, and the drain terminal 306 of theESD protection device 300 is electrically connected to the drainterminal 106 of the micro-switch 100.

[0043] In this first example, the ESD protection device 300 is employedto protect the drain terminal 106 of the micro-switch 100 from theadverse effects of the ESD event. Like the contact portion 308 c of theESD protection device 300, at least the tip of the contact portion 108 cof the micro-switch 100 overhangs the drain contacts 106 a-106 b.Accordingly, in order to protect the drain terminal 106 of themicro-switch 100 from damage, the overlap area of the drain contacts 306a-306 b of the ESD protection device 300 is made larger than thecorresponding overlap area of the drain contacts 106 a-106 b of themicro-switch 100.

[0044] Because, in this first example, the drain terminal 306 of the ESDprotection device 300 is electrically connected to the drain terminal106 of the micro-switch 100, a pull-in voltage generated at the drainterminal 106, in response to the ESD event, causes respective electricfields to be established in the spaces between the contact portion 308 cand the drain contacts 306 a-306 b of the ESD protection device 300, andbetween the contact portion 108 c and the drain contacts 106 a-106 b ofthe micro-switch 100. Further, because the overlap area of the draincontacts 306 a-306 b is configured to be larger than the correspondingoverlap area of the drain contacts 106 a-106 b, the magnitude of therespective electric field established in the ESD protection device 300is greater than that of the respective electric field established in themicro-switch 100.

[0045] Because the electric field established in the ESD protectiondevice 300 is stronger than the electric field established in themicro-switch 100, the electric field of the ESD protection device 300reaches a threshold value before the electric field of the micro-switch100, thereby causing the two (2) terminal switch of the ESD protectiondevice 300 to close before the micro-switch 100. In a preferredembodiment, the overlap area of the drain contacts 306 a-306 b isdetermined to close the two (2) terminal switch of the ESD protectiondevice 300 at a predetermined level of the pull-in voltage generated inresponse to the ESD event.

[0046] In an alternative embodiment, a spring constant or a massassociated with the beam 308 of the ESD protection device 300 may beconfigured to cause the two (2) terminal switch of the ESD protectiondevice 300 to close before the micro-switch 100.

[0047] It should be understood that the ESD protection device 300 may besimilarly employed to protect other devices such as the micro-relay 200(see FIGS. 2a-2 b) from adverse effects of ESD events.

[0048] In. the illustrated embodiment, the drain contacts 306 a-306 b ofthe ESD protection device 300 are configured to resist damage from theESD event by current-limiting drain resistors 310 a-310 b coupledbetween the respective drain contacts 306 a-306 b and the drain terminal306. For example, the drain resistors 310 a-310 b may be made ofpolysilicon or any other suitable material, and appropriate values ofthe drain resistors 310 a-310 b may be determined by the respectivelengths of the resistors.

[0049] In an alternative embodiment, the drain contacts 306 a-306 b aredisposed in respective primary conducting paths, a second set of draincontacts are disposed in respective high resistance paths in parallelwith the primary conducting paths, and the respective current-limitingdrain resistors 310 a-310 b are coupled between the second set of draincontacts and the drain terminal 306. Respective drain contact overlapareas associated with the drain contacts 306 a-306 b and the second setof drain contacts are configured to allow the high resistance paths toclose before the primary conducting paths, thereby allowing the primaryconducting paths to close safely to provide low resistance paths forcurrent flow. In other alternative embodiments, the drain contacts ofthe ESD protection device 300 are configured to withstand ESD events byincreasing the number of drain contacts and/or using alternate draincontact compositions. Increased numbers of drain contacts may also beprovided to prevent unwanted collapse of the ESD protection device 300.

[0050] It is noted that the ESD protection device 300 optionallyincludes a gate terminal 304 mounted to the substrate. The optional gateterminal 304 may be employed to make closure of the two (2) terminalswitch faster by suitably biasing the switch. Further, the optional gateterminal 304 may be employed to maintain actuation of the ESD protectiondevice 300 while the drain terminal 306 removes excess electrostaticcharge.

[0051] Still further, the optional gate terminal 304 of the ESDprotection device 300 may be electrically connected to, e.g., the gateterminal 104 of the micro-switch 100. An ESD event at the gate terminal104 may then cause a pull-in voltage to be generated at the gateterminal 304 to establish a threshold electric field in the spacebetween the contact portion 308 c of the beam 308 and the gate terminal304, thereby protecting the gate terminal 104 of the micro-switch 100.The drain terminal 106 of the micro-switch 100 may also be protected inthe event such a pull-in voltage at the drain terminal 106 is applied tothe optional gate terminal 304 of the ESD protection device 300.

[0052]FIG. 4 depicts a top view of a micro-switch 400 configured forreducing sensitivity to ESD, in accordance with the present invention.In the illustrated embodiment, the micro-switch 400 comprises a “rockerswitch” including a source terminal 402, a first gate terminal 404, asecond gate terminal 405, a first drain terminal 406, a second drainterminal 407, and a beam 408 mounted to a substrate (not shown). Thebeam 408 of the micro-switch 400 includes a fixed portion 408 a fixedlyattached to the source terminal 402 at approximately the middle of thebeam 408, a first flexure 408 b 1, a first contact portion 408 c 1 atleast the tip of which overhangs the drain contacts 406 a-406 b, asecond flexure 408 b 2, and a second contact portion 408 c 2 at leastthe tip of which overhangs the drain contacts 407 a-407 b.

[0053] The over-voltage factor of the micro-switch 400 is improved bymaking the main portion of the beam 408 rigid relative to the first andsecond flexures 408 b 1-408 b 2, by positioning the first gate terminal404 near the drain terminal 406 and positioning the drain contacts 406a-406 b in the area defined by the first gate terminal 404, and bypositioning the second gate terminal 405 near the drain terminal 407 andpositioning the drain contacts 407 a-407 b in the area defined by thesecond gate terminal 405.

[0054] According to the present invention, the micro-switch 400 isconfigured to be less sensitive to ESD events by using, e.g., the gateterminal 405 at one end of the rocker switch to latch that end of thedevice down. Such a configuration increases the pull-in voltage requiredto generate a threshold electric field to pull the other end of therocker switch down. It should be understood that the gate terminal 404may alternatively be used to latch one end of the rocker switch down toreduce the switch's sensitivity to ESD events.

[0055] Specifically, an appropriate pull-in voltage is applied at, e.g.,the gate terminal 405 to establish an electric field in the spacebetween the contact portion 408 c 2 of the beam 408 and the draincontacts 407 a-407 b of the drain terminal 407. When the electric fieldreaches a threshold value, the beam 408 deflects until the contactportion 408 c 2 comes into mechanical and electrical contact with thedrain contacts 407 a-407 b, thereby latching that end of the rockerswitch down. During operation, the other end of the rocker switchcomprising the contact portion 408 c 1 of the beam 408 and the draincontacts 406 a-406 b of the drain terminal 406 is used for selectivelycompleting the circuit between the source terminal 402 and the drainterminal 406.

[0056] The operation of the micro-switch 400 will be better understoodwith reference to the following second illustrative example. In thissecond example, it is understood that the gate terminal 405 is used tolatch one end of the rocker switch down to reduce the switch'ssensitivity to an ESD event. Accordingly, an appropriate first pull-involtage is applied at the gate terminal 405 to establish a thresholdelectric field to pull the contact portion 408 c 2 of the beam 408 intocontact with the drain contacts 407 a-407 b of the drain terminal 407.

[0057] Next, an appropriate second pull-in voltage is applied at thegate terminal 404 to establish an electric field to pull the contactportion 408 c 1 of the beam 408 into contact with the drain contacts 406a-406 b of the drain terminal 406.

[0058] Those of ordinary skill in this art will appreciate that theabove-described first and second pull-in voltages are normallyproportional to the square root of the overlap areas of the draincontacts 407 a-407 b and the drain contacts 406 a-406 b, respectively.Because the gate terminal 405 is used to latch one end of the rockerswitch down in response to the application of the first pull-in voltage,the second pull-in voltage associated with the gate terminal 404 isincreased. In this second example, for a tip ratio of 0.5, theelectrostatic force required to pull the contact portion 408 c 1 intocontact with the drain contacts 406 a-406 b is increased by a factor ofapproximately ±3, and the second pull-in voltage is increased by afactor of approximately 1.5.

[0059] It is noted that because the contact portion 408 c 2 is pulledinto contact with the drain contacts 407 a-407 b, the space between thecontact portion 408 c 1 and the drain contacts 406 a-406 b is typicallyincreased. In this second example, this increased spacing reduces theelectrostatic force on the drain terminal 406 by a factor ofapproximately 2.25. As a result, the second pull-in voltage associatedwith the gate terminal 404 is typically further increased by a factor ofapproximately 2.6, e.g., to more than 200 volts. Such an increase in thepull-in voltage of the micro-switch 400 significantly reduces theswitch's sensitivity to ESD.

[0060] The pull-in voltage of the micro-switch 400 may be furtherenhanced by, e.g., adding more drain contacts. Moreover, in this secondexample, the drain contacts 407 a-407 b may be omitted and bumpers maybe added between the contact portion 408 c 2 of the beam 408 and thegate terminal 405 to prevent the beam 408 and the gate terminal 405 fromcoming into contact.

[0061] It should be understood that the device of FIG. 4 may be suitablymodified to make a micro-relay with reduced sensitivity to ESD by, e.g.,increasing the number of drain terminals in the device from two (2) tofour (4).

[0062] The substrate of the ESD protection device 300 (see FIG. 3) andthe micro-switch 400 (see FIG. 4) may be made of glass, silicon, or anyother suitable substrate material. The beams 308 and 408 may be made ofgold, nickel, chromium, copper, iron and/or any other suitableconductive material. Further, the source terminals 302 and 402; the gateterminals 304, 404, and 405; and, the drain terminals 306, 406, and 407may be made of platinum, palladium, ruthenium, rhodium, gold or anyother suitable material. The terminals 302, 304, 306, 402, 404, 405,406, and 407 may be deposited on the respective substrates by anysuitable method such as sputtering or chemical vapor deposition.

[0063] Conventional micro-switches such as the micro-switch 100 (seeFIGS. 1a-1 b) may be ganged together to allow the micro-switches tohandle increased switching currents. FIG. 5 depicts a conventionalganged micro-switch 500 including a source terminal 502 comprising aplurality of source contacts 502.1-502.8, a gate terminal 504 comprisinga plurality of gate contacts 504.1-504.8, a drain terminal 506comprising a plurality of drain contacts 506.1-506.16, and a single beam508 comprising a plurality of beams 508.1-508.8 mounted to a substrate(not shown). The beams 508.1-508.8 are fixedly attached at theirproximal ends to a respective source contact, and overhang a respectivegate contact at their distal ends with at least their tips overhangingrespective drain contacts. The drain terminal 506 comprising theplurality of drain contacts 506.1-506.16 is electrically andmechanically connected to the respective beam when a large enoughelectrostatic force is established between the respective gate contactand the respective beam. It is noted that all contacts between therespective beams 508.1-508.8 and the respective drain contacts506.1-506.2, 506.3-506.4, 506.5-506.6, 506.7-506.8, 506.9-506.10,506.11-506.12, 506.13-506.14, and 506.15-506.16 are made or brokensimultaneously so that switching currents are shared between all of theswitches of the ganged micro-switch 500.

[0064]FIG. 6 depicts a conventional ganged micro-switch 600 including asource terminal 602, a gate terminal 604, a drain terminal 606, andmultiple beams 608 a-608 h mounted to a substrate (not shown). Theganged micro-switch 600 is like the ganged micro-switch 500 (see FIG. 5)with the exception that the ganged switch 600 comprises the multiplebeams 608 a-608 h while the ganged switch 500 comprises the single beam508.

[0065] It is noted that the ESD protection device 300 (see FIG. 3) maybe suitably configured, or a plurality of such ESD protection devicesmay be ganged together and electrically connected to the gangedmicro-switch 500 or the ganged micro-switch 600 to reduce the gangedswitches' sensitivity to ESD. It is further noted that conventionalmicro-relays such as the micro-relay 200 (see FIGS. 2a-2 b) may beganged together in the same manner as the ganged switches 500 and 600 toallow the micro-relays to handle increased currents.

[0066] The drain contacts of the ganged micro-switches 500 and 600 maybe configured to resist damage from ESD by including current-limitingdrain resistors coupled between the respective drain contacts and therespective drain terminals. For example, FIG. 7 depicts a gangedmicro-switch 700 that includes a source terminal 702, a gate terminal704, a beam 708, and respective drain resistors 710.1-710.16 coupledbetween respective drain contacts 706.1-706.16 and a drain terminal 706mounted to a substrate (not shown). Further, FIG. 8 depicts a gangedmicro-relay 800 that includes a source terminal 802, a gate terminal804, beams 808 a-808 h, respective drain resistors 810.1-810.8 coupledbetween respective drain contacts 806.1-806.8 and a first drain terminal806, and respective drain resistors 810.9-810.16 coupled betweenrespective drain contacts 807.1-807.8 and a second drain terminal 807mounted to a substrate (not shown). The drain resistors 710.1-710.16 and810.1-810.16 may be made of polysilicon or any other suitable material,and appropriate values of the drain resistors 710.1-710.16 and810.1-810.16 may be determined by the respective lengths of theresistors such that the drain contacts 706.1-706.16, 806.1-806.8, and807.1-807.8 have increased resistance to damage from ESD.

[0067] It should be understood that the drain contacts 706.1-706.16 ofthe ganged micro-switch 700 (see FIG. 7) may alternatively be disposedin respective primary conducting paths, a second set of drain contactsmay be disposed in respective high resistance paths in parallel with theprimary conducting paths, and respective current-limiting drainresistors may be coupled between the second set of drain contacts andthe drain terminal 706. Respective drain contact overlap areasassociated with the drain contacts 706.1-706.16 and the second set ofdrain contacts may then be configured to allow the high resistance pathsto close before the primary conducting paths, thereby allowing theprimary conducting paths to close safely to provide low resistance pathsfor current flow.

[0068] The drain contacts 806.1-806.8 and 807.1-807.8 of the gangedmicro-relay 800 (see FIG. 8) may similarly be disposed in respectiveprimary conducting paths, a second set of drain contacts may be disposedin respective high resistance paths in parallel with the primaryconducting paths, and respective current-limiting drain resistors may becoupled between the second set of drain contacts and the drain terminals806 and 807. Respective drain contact overlap areas associated with thedrain contacts 806.1-806.8 and 807.1-807.8 and the second set of draincontacts may then be configured to allow the high resistance paths toclose before the primary conducting paths to allow the primaryconducting paths to close safely and provide low resistance paths forcurrent flow.

[0069] It will further be appreciated by those of ordinary skill in theart that modifications to and variations of the above-describedapparatus and methods may be made without departing from the inventiveconcepts disclosed herein. Accordingly, the invention should not beviewed as limited except as by the scope and spirit of the appendedclaims.

What is claimed is:
 1. A protection device for providing electrostaticdischarge (ESD) protection to a micro-mechanical device, themicro-mechanical device including a first electrode and a secondelectrode mounted on a first substrate, and a first beam having a firstend attached to the first electrode and a second end overhanging thesecond electrode to define a first overlap area, the protection devicecomprising: a first terminal mounted on a second substrate andelectrically connectable to the first electrode of the micro-mechanicaldevice; a second terminal mounted on the second substrate andelectrically connectable to the second electrode of the micro-mechanicaldevice; and a second beam having a first end attached to the firstterminal and a second end overhanging at least a portion of the secondterminal when in a first position to define a second overlap area, thesecond beam being electro-statically deflectable in response to an ESDevent from the first position to a second position to make contact withthe second terminal, wherein the second overlap area is greater than thefirst overlap area.
 2. The protection device of claim 1 wherein thefirst substrate and the second substrate comprise the same substrate. 3.The protection device of claim 1 wherein the first end of the secondbeam includes at least one flexure attached to the first terminal. 4.The protection device of claim 1 wherein the first terminal comprises asource terminal and the second terminal comprises a drain terminal. 5.The protection device of claim 1 wherein the second overlap area isconfigured to allow the second beam to deflect from the first positionto the second position when the ESD event causes a predetermined voltagelevel to be applied at one of the first and second terminals.
 6. Theprotection device of claim 1 wherein the second terminal includes aterminal portion and at least one contact portion, and a respectiveresistive element is coupled between the terminal portion and the atleast one contact portion.
 7. The protection device of claim 1 whereinthe second terminal includes a terminal portion, at least one firstcontact portion, and at least one second contact portion, and arespective resistive element is coupled between the terminal portion andthe at least one second contact portion.
 8. The protection device ofclaim 1 further including a third terminal configured to apply a biasvoltage to the protection device.
 9. The protection device of claim 8wherein the third terminal comprises a gate terminal.
 10. The protectiondevice of claim 1 wherein the micro-mechanical device comprises amicro-switch.
 11. The protection device of claim 1 wherein themicro-mechanical device comprises a micro-relay.
 12. The protectiondevice of claim 1 wherein the micro-mechanical device further includes athird electrode mounted on the first substrate, and the second terminalof the protection device is electrically connectable to the thirdelectrode.
 13. The protection device of claim 1 wherein the second beamhas an associated spring constant, and the associated spring constant isdetermined to increase the speed of deflection of the second beam. 14.The protection device of claim 1 wherein the second beam has anassociated mass, and the associated mass is determined to increase thespeed of deflection of the second beam.
 15. A micro-mechanical deviceconfigured to be less sensitive to electrostatic discharge (ESD) events,comprising: a first pair of terminals mounted on a substrate; a secondpair of terminals mounted on the substrate; a center terminal mounted onthe substrate between the first and second pairs of terminals; and abeam having a center portion attached to the center terminal, a firstend being deflected to make contact with a first terminal of the firstterminal pair by an electrostatic field established between the firstend and a second terminal of the first terminal pair, and a second endoverhanging the second terminal pair when in a first position and beingdeflectable to make contact with a first terminal of the second terminalpair by an electrostatic field established between the second end and asecond terminal of the second terminal pair, wherein the first end ofthe beam is deflected so as to increase a pull-in voltage required topull the second end of the beam into contact with the first terminal ofthe second terminal pair, thereby reducing the sensitivity of the deviceto ESD events.
 16. The micro-mechanical device of claim 15 furtherincluding at least one first flexure attached to the center terminal anddisposed between the first end and the center terminal, and at least onesecond flexure attached to the center terminal and disposed between thesecond end and the center terminal.
 17. The micro-mechanical device ofclaim 15 wherein the center terminal comprises a source terminal, thefirst terminals of the first and second terminal pairs compriserespective drain terminals, and the second terminals of the first andsecond terminal pairs comprise respective gate terminals.
 18. Themicro-mechanical device of claim 15 wherein the micro-mechanical devicecomprises a micro-switch.
 19. The micro-mechanical device of claim 15wherein the micro-mechanical device comprises a micro-relay.
 20. Themicro-mechanical device of claim 19 further including an insulatordisposed between the second end of the beam and the center portion ofthe beam.